The invention relates to an insulation assembly designed for thermal protection of a structure submitted to conditions of intense thermal aggression.
Many protection systems are available to maintain a structure at a permissible temperature when the structure is submitted to conditions of intense thermal aggression for a variable length of time. These protections can be classified in three different categories according to their mode of action: active protection, semiactive protection, passive protection.
Active protections consist of insulation integrating active material designed to vaporize or transpire during heating of the shield. These protections, such as those described in French patent Nos. 2 061 509, 2 512 169, 2 547 895 and 2 592 131, globally stabilize the temperature of the structure to be protected at the vicinity of the vaporization or transpiration temperature of the active material (approximately 100.degree. C. in the case of water). They then act as ordinary insulators. It can be seen that the temperature rise of the structure is non-negligible. In addition, the protection is effective only as long as the active material is not totally depleted. Therefore, in the case of fire, there is a risk of a lack of active material whose role and function are essential with regard to the efficiency of the protection. The solution to this problem, consisting of recirculating, in the case of water, the superheated steam after condensing it, or reinjecting the water (or selected liquid) as it evaporates, is moreover not suitable in all cases.
As for semiactive protections, they consist of ablative materials of medium specific gravity (approximately 1.7) such as, for instance, a carbon-carbon composite consisting of fibers or a carbon fabric embedded in a carbon matrix. Although offering good protection, these materials have two major drawbacks. First of all, they are radiating external insulators or ablative materials above a certain temperature. Accordingly, as above, the protection decreases as the shield is consumed (for instance by burning). Furthermore, such shields are relatively costly.
Finally, passive protections include the many external insulation systems obtained by various associations of protective coatings based on refractory fibers, quartz or silica wools, various honeycomb materials or reflecting screen systems. Currently, however, no passive protection capable of preventing the internal temperature rise of a structure maintained in a fire for at least one hour exists with an acceptable specific weight and cost.